Cellphones and driving: As dangerous as we think?

"Frankly, we're skeptical that a ban on handheld (phones) would have that big of an impact because there's not really a difference in the level of distraction. "What we found was that 40 percent of drivers say that they are using their cellphones much less or not at all, or they've given it up entirely. So there is a sizable portion of the motoring public that have given up cellphone use or markedly cut back."

A 2010 survey conducted by the National Highway Transportation Safety Administration asked more than 6,000 drivers to describe their cellphone use behind the wheel and their perception of how it affected their driving ability.

The survey found that nearly 77 percent were likely to answer an incoming call while driving, but only 41 percent placed outgoing calls. A little more than half said they didn't believe talking on a handheld device had any effect on their driving, though about 20 percent said they tended to drive slower while on the phone.

Several recent studies have questioned if cellphone use is a grave danger to motorists, including one released this year by University of Chicago economics professor Saurabh Bhargava and Vikram Pathania, of the London School of Economics.

The study used a widespread feature of cellphone carriers in the previous decade — the 9 p.m. rate discount — to measure whether drivers were more likely to crash while on the phone. A comparison of hundreds of thousands of calls made just before and just after 9 p.m. against crash data found that while call volumes increased when rates became cheaper, there was no corresponding rise in the number of accidents. Researchers looked at calls that went from cell tower to cell tower, indicating the caller was moving at the time.

"Most people are convinced that using cellphones while driving is dangerous," Bhargava said Thursday. "What we find flies in the face of the prevalent viewpoint. Despite a rise in driver call volume of about 7 percent, we find no rise in the relative crash rate."

Bhargava said their study does not discount that cellphones pose a distraction for drivers, but said that many of the more well-known studies failed to account for two main variables: some drivers who are naturally more careful while on the phone and others who are poor drivers whether they're on the phone or not.

"So one explanation for our result is that cellphones may be dangerous, but drivers are aware of the danger and drive more slowly or only use their cell in situations that are safe. They regulate themselves," Bhargava said. "Another possible explanation is that there is a set of risk-loving drivers out there who, if they weren't using their cellphones, might be involved in other distracting activities, such as playing with the radio."

Another recent study examined call and crash data collected by General Motorssubsidiary OnStar, which provides hands-free cellphone calling in vehicles equipped with the system. The system also automatically calls the OnStar customer service representatives when a driver's vehicle is involved in an accident severe enough to deploy the air bags.

The study, conducted in 2009by researchers from Wayne State University,examined more than 91million callsmade on the OnStar hands-free system by nearly 324,000drivers over the course of 21/2 years.

The study found that drivers using OnStar's hands-free system experienced about fiveair bag deployments per 100million minutes of driving, while those who were not using the system to make calls had a little more than eightair bag deployments per 100 million minutes of driving.

Researchers concluded that drivers who used hands-free devices faced little to no more risk of an accident than those who weren't on the phone, in marked contrast to previous studies that placed the risk at four times greater.

But the study was later criticized for failing to factor in the possibility that many of the study's drivers may have been using a conventional cellphone when they had an accident causing air bags to deploy.